The present disclosure relates to an image forming apparatus that includes a discharge tray for receiving printed sheets of paper and detects full of the discharge tray.
An image forming apparatus such as a multifunction peripheral, a printer, or a copier is equipped with a discharge tray for receiving printed sheets of paper. There is a limitation of amount (thickness or the number) of sheets of paper that can be stacked on the discharge tray. When sheets of paper are stacked up to a height of a discharging opening for sheet, the stacked sheets of paper may abut a sheet of paper to be discharged next, and hence the discharge thereof is blocked. As a result, jamming of the sheet may occur at the discharging opening portion. In order to prevent such a bad situation, full of the discharge tray may be detected.
There is known an image forming apparatus that detects full of the discharge tray as described below. Specifically, the image forming apparatus performs an image forming process on a plurality of sets of sheets of paper, feeds and conveys the sheets of paper to a compiler tray, outputs a control signal instructing post processing or discharge processing in a period from feeding of the final sheet of paper of one set to feeding of the first sheet of paper of the next set, responds to the control signal so as to perform the post processing on the sheets of paper conveyed to the compiler tray and discharges the sheets of paper to the discharge tray, detects that stacking height of the sheets of paper on the discharge tray has exceeded a permissible stacking height (i.e., detects full of the discharge tray), and outputs a full signal indicating that the discharge tray is full when detecting the full of the discharge tray at the time point when the control signal is received, and stops to feed the first sheet of paper of the next set when receiving the full signal. The full signal is transmitted only in a break between the sets. A false detection of temporary excessing the permissible stacking amount due to curling of the sheet of paper during the process of setting sheets of paper is ignored. This is for a purpose to avoid interruption of the image forming process and to prevent a false detection of excess of the stacking amount on the discharge tray.
As described above as the known technique, it is common to provide the discharge tray with a sensor so as to detect full of the discharge tray. However, when the sensor for detecting full of the discharge tray and a mechanism working in accordance with amount of sheets of paper stacked on the discharge tray are provided, manufacturing cost of the image forming apparatus increases, and the manufacturing process becomes complicated. In order to reduce manufacturing cost of the image forming apparatus, instead of disposing the sensor and the mechanism for detecting full of the discharge tray, the number of sheets of paper discharged onto the discharge tray may be counted so as to detect full of the discharge tray. For instance, the upper limit number of sheets is determined in advance by considering the design number of sheets of paper that can be stacked on the discharge tray. Then, the number of sheets from start of a printing job is counted (integrated). When the count value reaches an upper limit number of sheets, full of the discharge tray is detected.
Here, an actual thickness of the sheets of paper on the discharge tray varies depending on amount of curl (degree of curl) of discharged sheets of paper. In addition, the amount of curl (state of curl) is related to amount of toner used for the printed image, and the like. For this reason, the amount of curl is affected by content of print and is different for each sheet of paper.
Conventionally, when detecting full of the discharge tray by counting the number of sheets, the apparatus merely and literally counts the number of sheets. Accordingly, there is a problem that the amount of curl (degree of curl) of each sheet of paper is not considered for processing. As a result, in the image forming apparatus of this type that detects full of the discharge tray by counting the number of sheets, sheets of paper stacked on the discharge tray may block the discharging opening for a sheet of paper before the count value reaches the upper limit number of sheets because of a curl of a sheet of paper. When the discharging opening is blocked, jamming of the sheet occurs so that the stacked sheets of paper are disturbed.
It is considered to intentionally set the upper limit number of sheets to a substantially small value so that the discharging opening is not blocked even if the amount of curl is large in detecting full of the discharge tray by counting the number of sheets. However, the number of sheets that can be stacked on the discharge tray is substantially reduced, and hence full of the discharge tray is detected in a state where more sheets of paper can be stacked.
Here, the known image forming apparatus described above, which detects full of the discharge tray by using an actuator or a sensor, is not the type that counts the number of discharged sheets of paper, and therefore cannot solve the above-mentioned problem. In addition, there is a problem that manufacturing cost of the image forming apparatus is higher than that of the type that detects full of the discharge tray by counting the number of sheets.